//-------------------------------------------------------------------------//
//          Windows Graphics Programming: Win32 GDI and DirectDraw         //
//                        ISBN  0-13-086985-6                              //
//                                                                         //
//  Modified by: Yuan, Feng                             www.fengyuan.com   //
//  Changes    : C++, exception, in-memory source, BGR byte order          //
//  Version    : 1.00.000, May 31, 2000                                    //
//-------------------------------------------------------------------------//

/*
 * jdhuff.c
 *
 * Copyright (C) 1991-1997, Thomas G. Lane.
 * This file is part of the Independent JPEG Group's software.
 * For conditions of distribution and use, see the accompanying README file.
 *
 * This file contains Huffman entropy decoding routines.
 *
 * Much of the complexity here has to do with supporting input suspension.
 * If the data source module demands suspension, we want to be able to back
 * up to the start of the current MCU.  To do this, we copy state variables
 * into local working storage, and update them back to the permanent
 * storage only upon successful completion of an MCU.
 */

#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
#include "jdhuff.h"		/* Declarations shared with jdphuff.c */


/*
 * Expanded entropy decoder object for Huffman decoding.
 *
 * The savable_state subrecord contains fields that change within an MCU,
 * but must not be updated permanently until we complete the MCU.
 */

typedef struct {
  int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */
} savable_state;

/* This macro is to work around compilers with missing or broken
 * structure assignment.  You'll need to fix this code if you have
 * such a compiler and you change MAX_COMPS_IN_SCAN.
 */

#ifndef NO_STRUCT_ASSIGN
#define ASSIGN_STATE(dest,src)  ((dest) = (src))
#else
#if MAX_COMPS_IN_SCAN == 4
#define ASSIGN_STATE(dest,src)  \
	((dest).last_dc_val[0] = (src).last_dc_val[0], \
	 (dest).last_dc_val[1] = (src).last_dc_val[1], \
	 (dest).last_dc_val[2] = (src).last_dc_val[2], \
	 (dest).last_dc_val[3] = (src).last_dc_val[3])
#endif
#endif


typedef struct {
  struct jpeg_entropy_decoder pub; /* public fields */

  /* These fields are loaded into local variables at start of each MCU.
   * In case of suspension, we exit WITHOUT updating them.
   */
  bitread_perm_state bitstate;	/* Bit buffer at start of MCU */
  savable_state saved;		/* Other state at start of MCU */

  /* These fields are NOT loaded into local working state. */
  unsigned int restarts_to_go;	/* MCUs left in this restart interval */

  /* Pointers to derived tables (these workspaces have image lifespan) */
  d_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS];
  d_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS];

  /* Precalculated info set up by start_pass for use in decode_mcu: */

  /* Pointers to derived tables to be used for each block within an MCU */
  d_derived_tbl * dc_cur_tbls[D_MAX_BLOCKS_IN_MCU];
  d_derived_tbl * ac_cur_tbls[D_MAX_BLOCKS_IN_MCU];
  /* Whether we care about the DC and AC coefficient values for each block */
  boolean dc_needed[D_MAX_BLOCKS_IN_MCU];
  boolean ac_needed[D_MAX_BLOCKS_IN_MCU];
} huff_entropy_decoder;

typedef huff_entropy_decoder * huff_entropy_ptr;


/*
 * Initialize for a Huffman-compressed scan.
 */

void start_pass_huff_decoder (j_decompress_ptr cinfo)
{
  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
  int ci, blkn, dctbl, actbl;
  jpeg_component_info * compptr;

  /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
   * This ought to be an error condition, but we make it a warning because
   * there are some baseline files out there with all zeroes in these bytes.
   */
  if (cinfo->Ss != 0 || cinfo->Se != DCTSIZE2-1 ||
      cinfo->Ah != 0 || cinfo->Al != 0)
    cinfo->WARNMS(JWRN_NOT_SEQUENTIAL);

  for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
    compptr = cinfo->cur_comp_info[ci];
    dctbl = compptr->dc_tbl_no;
    actbl = compptr->ac_tbl_no;
    /* Compute derived values for Huffman tables */
    /* We may do this more than once for a table, but it's not expensive */
    jpeg_make_d_derived_tbl(cinfo, TRUE, dctbl,
			    & entropy->dc_derived_tbls[dctbl]);
    jpeg_make_d_derived_tbl(cinfo, FALSE, actbl,
			    & entropy->ac_derived_tbls[actbl]);
    /* Initialize DC predictions to 0 */
    entropy->saved.last_dc_val[ci] = 0;
  }

  /* Precalculate decoding info for each block in an MCU of this scan */
  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
    ci = cinfo->MCU_membership[blkn];
    compptr = cinfo->cur_comp_info[ci];
    /* Precalculate which table to use for each block */
    entropy->dc_cur_tbls[blkn] = entropy->dc_derived_tbls[compptr->dc_tbl_no];
    entropy->ac_cur_tbls[blkn] = entropy->ac_derived_tbls[compptr->ac_tbl_no];
    /* Decide whether we really care about the coefficient values */
    if (compptr->component_needed) {
      entropy->dc_needed[blkn] = TRUE;
      /* we don't need the ACs if producing a 1/8th-size image */
      entropy->ac_needed[blkn] = (compptr->DCT_scaled_size > 1);
    } else {
      entropy->dc_needed[blkn] = entropy->ac_needed[blkn] = FALSE;
    }
  }

  /* Initialize bitread state variables */
  entropy->bitstate.bits_left = 0;
  entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */
  entropy->pub.insufficient_data = FALSE;

  /* Initialize restart counter */
  entropy->restarts_to_go = cinfo->restart_interval;
}


/*
 * Compute the derived values for a Huffman table.
 * This routine also performs some validation checks on the table.
 *
 * Note this is also used by jdphuff.c.
 */

GLOBAL(void)
jpeg_make_d_derived_tbl (j_decompress_ptr cinfo, boolean isDC, int tblno,
			 d_derived_tbl ** pdtbl)
{
  JHUFF_TBL *htbl;
  d_derived_tbl *dtbl;
  int p, i, l, si, numsymbols;
  int lookbits, ctr;
  char huffsize[257];
  unsigned int huffcode[257];
  unsigned int code;

  /* Note that huffsize[] and huffcode[] are filled in code-length order,
   * paralleling the order of the symbols themselves in htbl->huffval[].
   */

  /* Find the input Huffman table */
  if (tblno < 0 || tblno >= NUM_HUFF_TBLS)
    cinfo->ERREXIT1(JERR_NO_HUFF_TABLE, tblno);
  htbl =
    isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno];
  if (htbl == NULL)
    cinfo->ERREXIT1(JERR_NO_HUFF_TABLE, tblno);

  /* Allocate a workspace if we haven't already done so. */
  if (*pdtbl == NULL)
    *pdtbl = (d_derived_tbl *)
      cinfo->mem->alloc_small(JPOOL_IMAGE, sizeof(d_derived_tbl));
  dtbl = *pdtbl;
  dtbl->pub = htbl;		/* fill in back link */
  
  /* Figure C.1: make table of Huffman code length for each symbol */

  p = 0;
  for (l = 1; l <= 16; l++) {
    i = (int) htbl->bits[l];
    if (i < 0 || p + i > 256)	/* protect against table overrun */
      cinfo->ERREXIT(JERR_BAD_HUFF_TABLE);
    while (i--)
      huffsize[p++] = (char) l;
  }
  huffsize[p] = 0;
  numsymbols = p;
  
  /* Figure C.2: generate the codes themselves */
  /* We also validate that the counts represent a legal Huffman code tree. */
  
  code = 0;
  si = huffsize[0];
  p = 0;
  while (huffsize[p]) {
    while (((int) huffsize[p]) == si) {
      huffcode[p++] = code;
      code++;
    }
    /* code is now 1 more than the last code used for codelength si; but
     * it must still fit in si bits, since no code is allowed to be all ones.
     */
    if (((long) code) >= (((long) 1) << si))
      cinfo->ERREXIT(JERR_BAD_HUFF_TABLE);
    code <<= 1;
    si++;
  }

  /* Figure F.15: generate decoding tables for bit-sequential decoding */

  p = 0;
  for (l = 1; l <= 16; l++) {
    if (htbl->bits[l]) {
      /* valoffset[l] = huffval[] index of 1st symbol of code length l,
       * minus the minimum code of length l
       */
      dtbl->valoffset[l] = (long) p - (long) huffcode[p];
      p += htbl->bits[l];
      dtbl->maxcode[l] = huffcode[p-1]; /* maximum code of length l */
    } else {
      dtbl->maxcode[l] = -1;	/* -1 if no codes of this length */
    }
  }
  dtbl->maxcode[17] = 0xFFFFFL; /* ensures jpeg_huff_decode terminates */

  /* Compute lookahead tables to speed up decoding.
   * First we set all the table entries to 0, indicating "too long";
   * then we iterate through the Huffman codes that are short enough and
   * fill in all the entries that correspond to bit sequences starting
   * with that code.
   */

	memset(dtbl->look_nbits, 0, sizeof(dtbl->look_nbits));

  p = 0;
  for (l = 1; l <= HUFF_LOOKAHEAD; l++) {
    for (i = 1; i <= (int) htbl->bits[l]; i++, p++) {
      /* l = current code's length, p = its index in huffcode[] & huffval[]. */
      /* Generate left-justified code followed by all possible bit sequences */
      lookbits = huffcode[p] << (HUFF_LOOKAHEAD-l);
      for (ctr = 1 << (HUFF_LOOKAHEAD-l); ctr > 0; ctr--) {
	dtbl->look_nbits[lookbits] = l;
	dtbl->look_sym[lookbits] = htbl->huffval[p];
	lookbits++;
      }
    }
  }

  /* Validate symbols as being reasonable.
   * For AC tables, we make no check, but accept all byte values 0..255.
   * For DC tables, we require the symbols to be in range 0..15.
   * (Tighter bounds could be applied depending on the data depth and mode,
   * but this is sufficient to ensure safe decoding.)
   */
  if (isDC) {
    for (i = 0; i < numsymbols; i++) {
      int sym = htbl->huffval[i];
      if (sym < 0 || sym > 15)
	cinfo->ERREXIT(JERR_BAD_HUFF_TABLE);
    }
  }
}


/*
 * Out-of-line code for bit fetching (shared with jdphuff.c).
 * See jdhuff.h for info about usage.
 * Note: current values of get_buffer and bits_left are passed as parameters,
 * but are returned in the corresponding fields of the state struct.
 *
 * On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width
 * of get_buffer to be used.  (On machines with wider words, an even larger
 * buffer could be used.)  However, on some machines 32-bit shifts are
 * quite slow and take time proportional to the number of places shifted.
 * (This is true with most PC compilers, for instance.)  In this case it may
 * be a win to set MIN_GET_BITS to the minimum value of 15.  This reduces the
 * average shift distance at the cost of more calls to jpeg_fill_bit_buffer.
 */

#ifdef SLOW_SHIFT_32
#define MIN_GET_BITS  15	/* minimum allowable value */
#else
#define MIN_GET_BITS  (BIT_BUF_SIZE-7)
#endif

// Load up the bit buffer to a depth of at least nbits 
boolean bitread_working_state::jpeg_fill_bit_buffer(bit_buf_type get_buffer, int bits_left, int nbits)
{
	// Copy heavily used state fields into locals (hopefully registers)
	const JOCTET * next_input_byte  = m_next_input_byte;
	size_t bytes_in_buffer		    = m_bytes_in_buffer;
	j_decompress_ptr cinfo			= m_cinfo;

	/* Attempt to load at least MIN_GET_BITS bits into get_buffer. */
	/* (It is assumed that no request will be for more than that many bits.) */
	/* We fail to do so only if we hit a marker or are forced to suspend. */

	if (cinfo->unread_marker == 0) /* cannot advance past a marker */
	{
		while (bits_left < MIN_GET_BITS) 
		{
			/* Attempt to read a byte */
			if (bytes_in_buffer == 0) 
			{
				if (! cinfo->src->fill_input_buffer(cinfo))
					return FALSE;
				next_input_byte = cinfo->src->next_input_byte;
				bytes_in_buffer = cinfo->src->bytes_in_buffer;
			}
      
			bytes_in_buffer--;
			
			int c = GETJOCTET(*next_input_byte++);

			/* If it's 0xFF, check and discard stuffed zero byte */
			if (c == 0xFF) 
			{
				/* Loop here to discard any padding FF's on terminating marker,
				* so that we can save a valid unread_marker value.  NOTE: we will
				* accept multiple FF's followed by a 0 as meaning a single FF data
				* byte.  This data pattern is not valid according to the standard.
				*/
				do 
				{
					if (bytes_in_buffer == 0) 
					{
						if (! cinfo->src->fill_input_buffer(cinfo))
							return FALSE;
						next_input_byte = cinfo->src->next_input_byte;
						bytes_in_buffer = cinfo->src->bytes_in_buffer;
					}
					bytes_in_buffer--;
					c = GETJOCTET(*next_input_byte++);
				} 
				while (c == 0xFF);

				if (c == 0) 
				{
					/* Found FF/00, which represents an FF data byte */
					c = 0xFF;
				} 
				else 
				{
					/* Oops, it's actually a marker indicating end of compressed data.
					* Save the marker code for later use.
					* Fine point: it might appear that we should save the marker into
					* bitread working state, not straight into permanent state.  But
					* once we have hit a marker, we cannot need to suspend within the
					* current MCU, because we will read no more bytes from the data
					* source.  So it is OK to update permanent state right away.
					*/
					cinfo->unread_marker = c;
					/* See if we need to insert some fake zero bits. */
					goto no_more_bytes;
				}
			}

			/* OK, load c into get_buffer */
			get_buffer = (get_buffer << 8) | c;
			bits_left += 8;
		} /* end while */
	} 
	else 
	{
		no_more_bytes:
		/* We get here if we've read the marker that terminates the compressed
		* data segment.  There should be enough bits in the buffer register
		* to satisfy the request; if so, no problem.
		*/
		if (nbits > bits_left) 
		{
			/* Uh-oh.  Report corrupted data to user and stuff zeroes into
			* the data stream, so that we can produce some kind of image.
			* We use a nonvolatile flag to ensure that only one warning message
			* appears per data segment.
			*/
			if (! cinfo->entropy->insufficient_data) 
			{
				cinfo->WARNMS(JWRN_HIT_MARKER);
				cinfo->entropy->insufficient_data = TRUE;
			}
			/* Fill the buffer with zero bits */
			get_buffer <<= MIN_GET_BITS - bits_left;
			bits_left = MIN_GET_BITS;
		}
	}

	/* Unload the local registers */
	m_next_input_byte = next_input_byte;
	m_bytes_in_buffer = bytes_in_buffer;
	m_get_buffer = get_buffer;
	m_bits_left = bits_left;

	return TRUE;
}


/*
 * Out-of-line code for Huffman code decoding.
 * See jdhuff.h for info about usage.
 */

int bitread_working_state::jpeg_huff_decode (bit_buf_type get_buffer, int bits_left, d_derived_tbl * htbl, int min_bits)
{
	register int i = min_bits;
	register long code;

	/* HUFF_DECODE has determined that the code is at least min_bits */
	/* bits long, so fetch that many bits in one swoop. */

/*	if ( bits_left>16 )
	{
		code = GET_BITS(i);

		// Collect the rest of the Huffman code one bit at a time. 
		// This is per Figure F.16 in the JPEG spec. 

		while (code > htbl->maxcode[i]) 
		{
			code = (code << 1) | GET_BITS(1);
			i++;
		}

	}
	else */
	{
		if ( ! CHECK_BIT_BUFFER(i, bits_left, get_buffer) )
			return -1;
	
		code = GET_BITS(i);

		/* Collect the rest of the Huffman code one bit at a time. */
		/* This is per Figure F.16 in the JPEG spec. */

		while (code > htbl->maxcode[i]) 
		{
			code <<= 1;
		
			if ( ! CHECK_BIT_BUFFER(1, bits_left, get_buffer ) )
				return -1;
		
			code |= GET_BITS(1);
			i++;
		}
	}

	/* Unload the local registers */
	m_get_buffer = get_buffer;
	m_bits_left  = bits_left;

	/* With garbage input we may reach the sentinel value l = 17. */

	if (i > 16) 
	{
		m_cinfo->WARNMS(JWRN_HUFF_BAD_CODE);
		return 0;			/* fake a zero as the safest result */
	}

	return htbl->pub->huffval[ (int) (code + htbl->valoffset[i]) ];
}


/*
 * Figure F.12: extend sign bit.
 * On some machines, a shift and add will be faster than a table lookup.
 */

#ifdef AVOID_TABLES

#define HUFF_EXTEND(x,s)  ((x) < (1<<((s)-1)) ? (x) + (((-1)<<(s)) + 1) : (x))

#else

#define HUFF_EXTEND(x,s)  ((x) < extend_test[s] ? (x) + extend_offset[s] : (x))

static const int extend_test[16] =   /* entry n is 2**(n-1) */
  { 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080,
    0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 };

static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */
  { 0, ((-1)<<1) + 1, ((-1)<<2) + 1, ((-1)<<3) + 1, ((-1)<<4) + 1,
    ((-1)<<5) + 1, ((-1)<<6) + 1, ((-1)<<7) + 1, ((-1)<<8) + 1,
    ((-1)<<9) + 1, ((-1)<<10) + 1, ((-1)<<11) + 1, ((-1)<<12) + 1,
    ((-1)<<13) + 1, ((-1)<<14) + 1, ((-1)<<15) + 1 };

#endif /* AVOID_TABLES */


/*
 * Check for a restart marker & resynchronize decoder.
 * Returns FALSE if must suspend.
 */

LOCAL(boolean)
process_restart (j_decompress_ptr cinfo)
{
  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
  int ci;

  /* Throw away any unused bits remaining in bit buffer; */
  /* include any full bytes in next_marker's count of discarded bytes */
  cinfo->marker->discarded_bytes += entropy->bitstate.bits_left / 8;
  entropy->bitstate.bits_left = 0;

  /* Advance past the RSTn marker */
  if (! (*cinfo->marker->read_restart_marker) (cinfo))
    return FALSE;

  /* Re-initialize DC predictions to 0 */
  for (ci = 0; ci < cinfo->comps_in_scan; ci++)
    entropy->saved.last_dc_val[ci] = 0;

  /* Reset restart counter */
  entropy->restarts_to_go = cinfo->restart_interval;

  /* Reset out-of-data flag, unless read_restart_marker left us smack up
   * against a marker.  In that case we will end up treating the next data
   * segment as empty, and we can avoid producing bogus output pixels by
   * leaving the flag set.
   */
  if (cinfo->unread_marker == 0)
    entropy->pub.insufficient_data = FALSE;

  return TRUE;
}


/*
 * Decode and return one MCU's worth of Huffman-compressed coefficients.
 * The coefficients are reordered from zigzag order into natural array order,
 * but are not dequantized.
 *
 * The i'th block of the MCU is stored into the block pointed to by
 * MCU_data[i].  WE ASSUME THIS AREA HAS BEEN ZEROED BY THE CALLER.
 * (Wholesale zeroing is usually a little faster than retail...)
 *
 * Returns FALSE if data source requested suspension.  In that case no
 * changes have been made to permanent state.  (Exception: some output
 * coefficients may already have been assigned.  This is harmless for
 * this module, since we'll just re-assign them on the next call.)
 */

boolean decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{
  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
  int blkn;
  BITREAD_STATE_VARS;
  savable_state state;

  /* Process restart marker if needed; may have to suspend */
  if (cinfo->restart_interval) {
    if (entropy->restarts_to_go == 0)
      if (! process_restart(cinfo))
	return FALSE;
  }

	// If we've run out of data, just leave the MCU set to zeroes.
	// This way, we return uniform gray for the remainder of the segment.
	
	if (! entropy->pub.insufficient_data) 
	{
	    /* Load up working state */
		BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
		ASSIGN_STATE(state, entropy->saved);

		// Outer loop handles each block in the MCU

		for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) 
		{
			JBLOCKROW block = MCU_data[blkn];
			d_derived_tbl * dctbl = entropy->dc_cur_tbls[blkn];
			d_derived_tbl * actbl = entropy->ac_cur_tbls[blkn];
			register int s, k, r;

			/* Decode a single block's worth of coefficients */

			/* Section F.2.2.1: decode the DC coefficient difference */
			if ( ! br_state.HUFF_DECODE(s, bits_left, get_buffer, dctbl) )
				return FALSE;
      
			if (s) 
			{
				if ( ! br_state.CHECK_BIT_BUFFER(s, bits_left, get_buffer) )
					return FALSE;
				
				r = GET_BITS(s);
				s = HUFF_EXTEND(r, s);
			}

			if (entropy->dc_needed[blkn]) 
			{
				/* Convert DC difference to actual value, update last_dc_val */
				int ci = cinfo->MCU_membership[blkn];
				s += state.last_dc_val[ci];
				state.last_dc_val[ci] = s;
				/* Output the DC coefficient (assumes jpeg_natural_order[0] = 0) */
				(*block)[0] = (JCOEF) s;
			}

			if (entropy->ac_needed[blkn]) 
			{

				/* Section F.2.2.2: decode the AC coefficients */
				/* Since zeroes are skipped, output area must be cleared beforehand */
				
				for (k = 1; k < DCTSIZE2; k++) 
				{
					if ( ! br_state.HUFF_DECODE(s, bits_left, get_buffer, actbl) )
						return FALSE;
      
					r = s >> 4;
					s &= 15;
      
					if (s) 
					{
						k += r;
						
						if ( ! br_state.CHECK_BIT_BUFFER(s, bits_left, get_buffer) )
							return FALSE;
						
						r = GET_BITS(s);
						s = HUFF_EXTEND(r, s);
						/* Output coefficient in natural (dezigzagged) order.
						* Note: the extra entries in jpeg_natural_order[] will save us
						* if k >= DCTSIZE2, which could happen if the data is corrupted.
						*/
						(*block)[jpeg_natural_order[k]] = (JCOEF) s;
					} 
					else 
					{
						if (r != 15)
							break;
						k += 15;
					}
				}
			} 
			else 
			{
				/* Section F.2.2.2: decode the AC coefficients */
				/* In this path we just discard the values */
				for (k = 1; k < DCTSIZE2; k++) 
				{
					if ( ! br_state.HUFF_DECODE(s, bits_left, get_buffer, actbl) )
						return FALSE;
      
					r = s >> 4;
					s &= 15;
      
					if (s) 
					{
						k += r;
						
						if ( ! br_state.CHECK_BIT_BUFFER(s, bits_left, get_buffer) )
							return FALSE;
						
						DROP_BITS(s);
					} 
					else 
					{
						if (r != 15)
							break;
						k += 15;
					}
				}
			}
		}

	    /* Completed MCU, so update state */
		BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
		ASSIGN_STATE(entropy->saved, state);
	}

	/* Account for restart interval (no-op if not using restarts) */
	entropy->restarts_to_go--;

	return TRUE;
}


/*
 * Module initialization routine for Huffman entropy decoding.
 */

GLOBAL(void)
jinit_huff_decoder (j_decompress_ptr cinfo)
{
	huff_entropy_ptr entropy;

	entropy = (huff_entropy_ptr)
		cinfo->mem->alloc_small(JPOOL_IMAGE, sizeof(huff_entropy_decoder));
	cinfo->entropy = (struct jpeg_entropy_decoder *) entropy;
	entropy->pub.start_pass = start_pass_huff_decoder;
	entropy->pub.decode_mcu = decode_mcu;

	/* Mark tables unallocated */
	for (int i = 0; i < NUM_HUFF_TBLS; i++) 
	{
		entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;
	}
}
